1. Field of the Invention
The present invention generally relates to a hydraulically actuated clutch release system for a motor vehicle friction clutch, including a piston-cylinder unit oriented concentrically to a transmission input shaft, whereby the cylinder of the piston-cylinder unit is fastened to the transmission housing, and between an inner and outer cylinder shell has the cylinder chamber for the piston, the shell of which is at least partly surrounded by a guide element.
2. Background Information
German Utility Model No. 93 13 557 discloses a clutch release system such as that described immediately above. Fastened to the piston of this clutch release system is a guide element which surrounds the piston, and which guides the piston in a sealed manner with respect to the external cylinder shell. Therefore, the guide element must essentially project in the axial direction a sufficient distance beyond the piston, so that this sealed connection can also remain reliably effective when the piston of a new friction clutch travels by, or over, its maximal extension out of the cylinder chamber.
Starting from this first extreme position, the piston executes a stroke into the cylinder chamber to engage the friction clutch. When there is wear in the friction clutch, accompanied by the corresponding action of the application spring of the friction clutch, the piston is also pushed deeper into the cylinder chamber, until the piston finally reaches a second extreme position. In the second extreme position, when the friction clutch is completely worn, the piston has reached its maximum depth of insertion into the cylinder chamber.
Because the length of the guide element is specified, or dictated, by addition, or superposition, of the stroke and wear travel of the piston, when determining the dimensions of the cylinder chamber in the axial direction, either the stroke distance of the piston must essentially be limited or a ring-like axial recess must essentially be formed on the cylinder housing radially outside a rotary shaft lip seal, into which recess the guide element can be inserted. The first-named measure, namely a limitation of the stroke distance of the piston, is usually not possible, since the stroke distance is specified as, or dictated by, a function of the design and layout of the friction clutch. The creation of a ring-like recess, as specified or dictated by the second measure can often be impossible in motor vehicles, in which, as a result of the design, there is essentially no space available for such a recess. Consequently, this known clutch release system can be unsuitable if a long piston stroke is demanded in a motor vehicle, where there is generally not much space available.